Retirement Benefits - Schedule of Net Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	$ 2,779.0
Plan assets at end of year	2,810.0	$ 2,779.0
Net amount on balance sheet consists of
Retirement benefits	(406.0)	(549.0)
Pension Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	3,078.0	2,751.0
Service cost	41.0	37.0	$ 42.0
Interest cost	136.0	147.0	150.0
Actuarial (gains) losses	(123.0)	322.0
Plan participant contributions	2.0	2.0
Benefits paid	(208.0)	(213.0)
Settlements and curtailments	(5.0)	(5.0)
Currency translation and other	10.0	37.0
Benefit obligation at end of year	2,931.0	3,078.0	2,751.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	2,779.0	2,457.0
Actual return on plan assets	143.0	464.0
Company contributions	88.0	27.0
Plan participant contributions	2.0	2.0
Benefits paid	(208.0)	(213.0)
Settlements	(4.0)	(5.0)
Currency translation and other	10.0	47.0
Plan assets at end of year	2,810.0	2,779.0	2,457.0
Funded status of plans	(121.0)	(299.0)
Net amount on balance sheet consists of
Other assets	222.0	184.0
Compensation and benefits	(20.0)	(19.0)
Retirement benefits	(323.0)	(464.0)
Net amount on balance sheet	(121.0)	(299.0)
Other Postretirement Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	45.0	46.0
Service cost	1.0	1.0	1.0
Interest cost	2.0	3.0	3.0
Actuarial (gains) losses	4.0	5.0
Plan participant contributions	5.0	4.0
Benefits paid	(15.0)	(13.0)
Settlements and curtailments	0.0	0.0
Currency translation and other	(1.0)	(1.0)
Benefit obligation at end of year	41.0	45.0	46.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Company contributions	10.0	9.0
Plan participant contributions	5.0	4.0
Benefits paid	(15.0)	(13.0)
Settlements	0.0	0.0
Currency translation and other	0.0	0.0
Plan assets at end of year	0.0	0.0	$ 0.0
Funded status of plans	(41.0)	(45.0)
Net amount on balance sheet consists of
Other assets	0.0	0.0
Compensation and benefits	(6.0)	(7.0)
Retirement benefits	(35.0)	(38.0)
Net amount on balance sheet	$ (41.0)	$ (45.0)